An imaging device for generating successive tomograms is used for obtaining information about the interior of the object examined. From the tomograms, valuable information about the position, the size or the structure of internal organs, of bone tissue or other soft tissue of a patient can be obtained, for example. In particular, the successive tomograms can also be recalculated in a three-dimensional representation.
Such an imaging device for recording successive tomograms can be, for example, an X-ray computer tomograph, a magnetic resonance tomograph, a photon emission computer tomograph or a positron emission tomograph. By the same token, such an imaging device can be constructed on the basis of ultrasound.
The contrast of the images of the object such as, for example of a patient, generated by such an imaging device, is produced by locally different properties of excitation, absorption, reflection or emission of the examined material compared with the radiation, particle radiation or sound waves used by the imaging device. In the case of an X-ray device, the different absorption or attenuation characteristics of different types of tissue are used for producing contrast. Since, for example, bone tissue and soft tissue differ greatly in the said characteristics, it is possible to analyze the structure of a bone of a patient on the basis of the associated contrast in the images.
Organs or vessels which do not significantly differ in the said characteristics for forming a contrast in the recorded images of surrounding tissue cannot be examined in a conventional manner due to the resultant contrast which is too low. When examining an organ through which blood circulates, for example a heart, a liver or a vessel in the area of the extremities of the patient, therefore, a contrast medium is introduced into the circulatory system of the patient before beginning the examination with the imaging device. As a consequence of the contrast medium, the examined organs are imaged with sufficiently high contrast compared with the surrounding tissue.
When generating tomograms with contrast medium administration, attention must be paid to the simultaneous presence of the contrast medium. For this purpose, it is becomes necessary to match the operating parameters of the imaging device and the propagation of the administered contrast medium in the patient to one another. For this purpose, a so-called scan protocol, in which operating parameters of the imaging device are stored for image recording, and a so-called contrast medium protocol in which parameters of a contrast medium administration are stored, are in each case selected matching one another for a desired area of examination.
In a scan protocol, for example, power values, the duration of the acting radiation, the radiation energy, a feed rate or a scan delay time, i.e. a delay time between individual tomogram recordings or between a monitoring and a recording phase are stored as operating parameters.
During the examination, the contrast medium is administered in accordance with the contrast medium protocol selected for the scan protocol, for example by means of a contrast medium device. Parameters for administering the contrast medium can be, for example, the concentration, the flow or the absolute quantity of contrast medium to be supplied. In particular, a contrast medium protocol can comprise a number of different administration phases which differ in the said parameters but also in the type of medium to be supplied. In complex contrast medium protocols, phases in which, for example, a sodium chloride solution is supplied, can also be arranged between phases in which contrast medium is administered.
The contrast medium protocol is used for generating a predictable contrast medium course in the patient so that during the recording of the successive tomograms, the contrast medium concentration required in each case for forming contrast is present in the area of examination. For example, a phase in which a sodium chloride solution is supplied is used for predictably stopping the course of contrast medium in time without loading the patient with too much contrast medium in an undesirable manner.
In practice, it disadvantageously frequently happens that contrast medium is still administered in accordance with the contrast medium protocol when this would no longer be necessary for recording the tomograms. This unwanted administration of additional quantity is of no additional use to the patient.